Thermal relay for starting fluorescent lamps



Oct. 17, 1944. c, HODGKINS 2,360,678

THERMAL RELAY FOR STARTING FLUORESCENT LAMPS Filed Dec. 16, 1942 lNVENTOR C l/JVOM/Yl/VS ATTORNEY Patented Oct. 17, 1944 THERMAL RELAY FOR STARTING FLUORESCENT LAMPS Charles H. Hodgkins, Fairfield, Conn., asslgnor to The Bryant Electric Company, Bridgeport, Conn., a corporation of Connecticut Application December 16, 1942, Serial No. 469,199

7 Claims.

The present invention relates to thermal relays and particularly to such relays for the starting of fluorescent lamps, and constitutes an improvement over that shown in copending application of R. F. Hays, Jr., and C. H. Hodgkins, Ser. N0. 396,576, filed June 4,' 1941, now Patent No. 2,313,745, issued March 16, 1943, ofwhich the present applicant is a co-inventor.

Fluorescent lamps are now well known in the art and are provided with a pair of'oppositely disposed thermionic electrodes which are initially heated to an electron-emitting temperature prior to actual starting of the lamp. Since a voltage higher than normal line voltage as supplied from the customary domestic source of supply is required to initiate a discharge, the relay first operates to close a heating circuit for the electrodes, after which the heating circuit is interrupted and a high voltage surge momentarily impressed across the preheated electron-emitting electrodes. Once the discharge has started in the lamp the relay remains dormant, but should the lamp fail to start upon the first operation of the relay, the latter continues in its cycle of operation until the lamp actually starts.

The difliculty heretofore existent in relays for starting lamps has been due to the rapidity of operation which in many instances does not allow sufiicient time to heat the electrodes of the lamp to full electron-emitting temperature. This results in the impression of the high voltage surge across the lamp electrodes prior to their reaching maximum electron-emitting temperature which causes sputtering of the electron-emitting coating provided on the surface of the electrodes, thus greatly reducing the useful life 01 the lamp.

It is accordingly an object of the present invention to provide a thermal relay for the starting of fluorescent lamps in which a sufllcient time delay occurs to insure adequate heating of the lamp electrodes and to prevent improper operation of the relay due to arcing at the contacts.

Another object of the present invention is the provision of a thermal relay particularly adaptable for starting of fluorescent lamps wherein positive engagement of the contact terminals is assured and chattering thereof eliminated as well as improper-operation of the relay due to arcing at the contacts.

Another object of the present invention is the provision or a thermal relay particularly'adaptable to the starting of fluorescent lamps wherein the relay operates with positiveness andis uninfluenced by ambient temperature and wherein undesirable operation of the relay is prevented which otherwise might result from arcing of the contacts.

A further object of the present invention is the provision of a thermal relay particularly adaptable to the starting of fluorescent lamps wherein the thermal element is prevented from twisting in an undesired direction and undesired operation'oi the relay due to arcing at the contacts is prevented.

Still further objects of thepresent invention 'will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Fig. 1 is a front elevatlonal view partly in cross section of the thermal relay of the present invention;

Fig. 2 is a side elevational view partly in cross section of the thermal relay unit shown in Fig. l with the elements in their normal position;

v Fig. 3 is a fragmentary sectional view taken on the line III-III of Fig. 1 and showing the relay in its normal or lamp-starting position;

Fig. 4 is a view similar to that shown in Fig. 3,

but showing the relay in the lamp-operating position;

Fig. 5 is a fragmentary sectional view similar to Fig. 3, but showing the position of the relay in the event excessive arcingat the contacts occurs; Fig. 6 is a fragmentary sectional view taken on the line VI-VI of Fig. 1, and s p Fig. 7 is a schematic diagram showing the connections of the relay in a circuit for the starting of a fluorescent lamp.

Referring now to the drawing in detail, a ther-, 'mal relay as shown in Fig. 1 comprises a base member 5 of suitable insulating material such as Bakelite, fiber or the like, secured 11339111 upright position to a closure member 8 also 01 insulating material, the latter of whichiorms-an end for an aluminum cylinder or can 1 being secured thereto by means of lugs: or the like 8. A U-shaped bimetallic element 9 is secured at the end or one leg to the base member 5 such as by a rivet or the like III, while. its other leg is provided with a suitable metallic contact terminal l2, such as silver, platinum or the like, positioned a short distance from the end thereof.

A similar contact terminal I3 is positioned to be normally engaged by the contact terminal H with the former being connected through a metallic connector ll to a socket terminal I5 carried by the closure member 6. The fixed leg of the bimetallic element 9 is provided with a corrugation l6 or substantially semi-cylindrical configuration and a heater element in the form of a resistance heater I 1 is, secured by suitable screws or rivets l8 and i9 to the base member beneath the corrugation IS. The cross piece or base portion 20 of the U-shaped bimetallic element 9 is provided with a stiffening rib 22 which may take the form of a small corrugation to prereadily from Figs. 1 and 6, one end of the heater I element 11 is connected to the bimetallic element 9 by-means of a metallic strip 25 on the rear side of the base 5 and by the rivet l0 which passes through the bimetallic element 9 and one end of the metallic strip 25. The other end of the heater element 11 is connected by a conductor 26 to one end of a glow relay tube 21 of the type such as shown and claimed in U. S. Patent 2,228,210, issued January 7, 1941, to R. F. Hays. Jr. I

The remaining electrode of the glow relay tube 21 is connected by a conductor 28 to an additional socket terminal 29 carried by the closure member 6. For the purpose of preventing interference with radio reception during operation of the fluorescent lamp, a small condenser 30 is connected in electrical parallel with the series-connected glow relay tube 21 and the thermal relay '3, a can be more readily appreciated by reference to Fig. 7. All of these v elements as shown are housed withinthe aluminum cylinder or can 1 so that an integral unit is formed which is readily insertable in an appropriate socket.

By reference now more particularly to Fig. '7, a circuit arrangement is shown for the starting of a fluorescent lamp 33 and in which the starting device in accordance with the present invention is employed. The lamp 33 is provided with oppositely disposed filamentary electrodes 34 and 35 which are connected in a series heating circuit by the starting device upon closure of a suitable switch 36. Upon closure of such switch 36 electrical energy will be supplied from the customary source of domestic potential Ll-L2 with current flowing through the filament 34 and a conductor 31, socket terminal 29 and conductor 28, to one 'of the electrodes of the glow relay tube 21.

. Substantially full line voltage is thus impressed across the electrodes, or contacts of the glow relay tube 21 since the circuit is completed through the conductor 26, heater element l1, bimetallic element 9. its normally closed contact terminals l2 and I3. metallic strip l4. socket terminal l5 and a conductor 38. filamentary electrode 35 and an inductance element 39, back to the opposite side of the source of supply L2.

As pointed out in the above-mentioned patent, the application of full line voltage across the electrodes of the glow relay tube will cause a glow discharge between its electrodes. This glow discharge heats the electrodes of the glow relay I tube and since one of the electrodes is a bia series heating circuit for the filamentary electrodes 34 and 35 of the lamp 33, thus heating such electrodes to an electron-emitting temperature. The bimetallic electrode of the glow relay tube 21 may be so designed that the PR effect is such that the flow of current in the heating circuit for the filamentary electrodes 34 and 35 is sufiicient to maintain the bimetallic electrode of the glow relay tube in a heated condition so it will continue in engagement with the other electrode of the glow relay tube.

0n the other hand, the glow relay tube need only be so designed that a high transient voltage will not be produced upon opening of its contacts. Since no high voltage surge is thus produced, premature opening of the electrodes of the glow relay causes no deleterious effect as they will again immediately close as long as full line voltage is impressed across the electrodes, which condition exists so long as the contacts l2 and I3 of the thermal relay 9 remain closed and the discharge is not initiated in the lamp 33. Closure of the heating circuit not only heats the filamentary electrodes 34 and 35, but since the heater element I1 is likewise in series in the circuit, it is also simultaneously heated. Consequently, by the time the filamentary electrodes 34 and 35 of the lamp 33 have reached optimum. electron-emitting temperature, the heater element l1 will likewise be heated to a temperature sufficient to cause operation: of the thermal re-, lay or bimetallic element 9 causing operation thereof with. attendant separation of its contacts l2 and I3, as hereinafter described more in detail.

This interrupts the heating circuit for the filamentary electrodes 34 and 35 and at the same time causes a high transient voltage surge from the inductance 39 which initiates a discharge between the heated electrodes 34 and 35 of the lamp 33. During operation of the lamp 33 the bimetallic element 9 consumes no energy from the source of supply, despite the fact that its contacts 12 and I3 again assume their normally closed position upon cooling of the bimetallic element 9 and heater element l1, and that the electrodes of the glow relay tube 21 likewise assume their normally open position upon cooling of the bimetallic electrode. This is because the voltage impressed across the electrodes of the glow relay tube during operation of the lamp 33 is insufiicient to again initiate a discharge in the glow relay tube 21.

If for any reason a discharge is not initiated in the lamp 33 upon opening of contacts i2 and I3 of "the thermal relay 9, the above described cycle will be repeated until such a discharge is initiated. The primary function of the bimetallic element 9 is to inject a time delay before its contacts l2 and I3 will open, such delayed action aflording the necessary time for the filamentary electrodes 34 and 35 of the lamp to heat. The construction shown promotes such delay in several ways. The semi-cylindrical portion I6 in the fixed leg is provided with a stiffening bead or corrugation IS in a peripheral relationship to the said portion 16 and in a longitudinal direction with respect to the leg. This bead prevents the portion I6 from bending and necessitates heat to travel by conduction therefrom .to the fiat portion of the leg before the leg will deflect due tothe heat. The semi-cylindrical portion may move bodily to and fro with respect to the heater when the flat portion of the leg defleets, but does not itself deflect. Thus time lag of heat transmission by conduction in the leg introduces one time delay action.

Additional delayed action is obtained by the requirement that the contact separating movement must be by conduction of heat toward the fixed end of the leg and since that end is in effect the short end of a lever, more force to overcome the inherent resilient tension acting in a contact-closing direction is required.

However, third and perhaps most important means for injecting time delay action in opening of contacts I2 and I3 is obtained by housing the heater within a ceramic or other tunnel orenclosure I1 which is shown best in Fig. 2. This enclosure I'I' may conveniently comprise a ceramic heat and electrical insulative tube seated lengthwise between rivets I8 and I9 transverse thereto and transverse to the bimetallic leg beneath the semi-cylindrical corrugation thereof parallel to said corrugation. The heater I I passes longitudinally through this tube or enclosure I1 and by virtue of the heat capacity of the enclosure, delayed action of heat from the heater to the bimetallic element 9 occurs. By these several means, therefore, ample delay of opening of contacts I2 and I3 is obtained to allow the lamp filaments to become heated and thegas in the lamp 33 ionized for assuring striking of the are immediately with first opening of said contacts.

Moreover, due to the time delay action of the bimetallic element 9 no damage is done to the lamp 33 because the thermal relay does not operate to open its contacts I2 and i3 until the filamentary electrodes 34 and 35 have been heated for a sufficient time'to bring them up to optimum thermionic emission. It should also be noted that the thermal relay 9 operates merely to interrupt the. series heating circuit, while the glow relay tube 21 operates to close such heating circuit. The heater element I! is so designed that the thermal relay opens its contacts only after the filamentary electrodes 34 and 35 have reached optimum electron-emitting temperature as above noted.

By reference now more particularly to Figs. 3

to 5, it will be noted, as before mentioned, that in the normal position of the bimetallic element 9 the contacts I2 and I3 are closed, as shown in Fig. 3. Also, due to the construction of the bimetallic element 9, a slight tension is applied to the movable leg carrying the contact I2 so that a positive engagement is established with the stationary contact I3. Upon heating the bimetallic element 9 by the heater element H, the fixed leg of the U-shaped bimetallic element will be distorted or deflected in the direction of the base member 9. This overcomes the tension or the movable leg in the opposite direction with the result that the contact I2 carried by the'movof the reinforced rib 22. Although slight heating of the movable leg of the bimetallic element 9 due to arcing at the contacts I2 and I3 is desirable to increase the contact pressure and eliminate chattering, too much heat would result in the contacts remaining closed for an objectionably long period of time, which condition might be injurious to the lamp auxiliaries, such as the glow switch 21 and the inductance 39, since they would be subjected to the relatively high starting current as long as the switch contacts remained closed.

able leg separates from the fixed contact I3. The

application of heat to the fixed leg of the U- shaped bimetallic element 9 is particularly advantageous because it contributes to the required time delay before opening of the contacts I2 and I3 occurs. Moreover, in the event the contacts I2 and I3 close under load with attendant generation ofheat at the contacts due to arcing, the

movable leg may be slightly heated by the contacts so as to increase the contact pressure, thus contributing to the desired time delay and at the same time eliminating chattering of the contacts. At the same time premature opening of these contacts by twisting or lateral movement of the bimetallic element is prevented by the provision To eliminate this possibility the movable leg of the bimetallic element 9 is provided at its end with an angularly disposed projection 40 normally spaced slightly from the base 5 when the contacts I2 and I3 are in their normally closed position, as shown in Fig. 3. Under normal heating conditions the contacts I2 and I3 will separate in the manner previously described and as shown in Fig. 4, which thus increases the spacing between the end of the projection 40 and the base 5. If; however, undue arcing between the contacts I2 and I3 occurs with resultant heating of the movable leg of the bimetallic element 9, it will deflect in the direction of the base until the projection 40 rests against the base 5 and deflection of this leg will continue until it assumes a bowed position, as shown more clearly in Fig. 5. To increase the arc of the how, a small pin or rod 42 is welded or" otherwise affixed to the underside of the movable leg of the bimetallic element 9 which functions as a fulcrum. Accordingly, excessive arcing with attendant heating of the movable leg of the bimetallic element 9 will cause sufllcient bowing thereof that the contacts I2 and I3 will be opened in the manner shown in Fig. 5, thus assuring separation of the contacts with causation of the high voltage surge from the inductance 39, as previously described, causing the initiation of a discharge in the lamp between the heated electrodes 34 and 35.

Although the relay 9 has thus far been described as forming an integral part of a complete starting unit in combination with a glow relay tube, in some instances it can itself be utilized and the glow relay tube entirely dispensed with, so that only the thermal relay and condenser remain in the casing.

It thus becomes obvious to those skilled'in the art that a thermal relay is herein provided particularly adaptable for the starting of fluorescent lamps wherein a desired time delay is provided so that its contacts remain closed and under tension for a predetermined period of time, after which separation of the contacts occurs without chattering. Moreover, the relay is so constructed that upon slight heating of the contacts due to arcing therebet-ween or other causes when closing under load, the contact tension is increased due to heat transfer from the contact carried by the bimetallic element to the movable leg thereof. If, however, undue arcing with excessive heating ensues, the movable leg of the biprising a heat-responsive element provided with an electric heater operable by current flow therethrough to cause heating of said heat-responsive element with attendant operation thereof after the lapse of a predetermined period of time to interrupt current flow through said heater, and means cooperating with said heat-responsive element to prevent heat generated by undue arcing upon interruption of current flow through said heater from causing undesired operation of said heat responsive element with attendant current flow through said heater.

2. A starting relay for discharge lamps comprising a thermal switch having a pair of normall closed contacts and a heat-responsive element an electric heater operable by current flow therelthrough upon closure of said contacts to cause heating of said heat-responsive element with attendant separation, of said contacts after the lapse of a predetermined period of time to interrupt current flow through said heater, and means cooperating with said heat-responsive element to prevent heat generated by undue arcing upon interruption of current flow through said heater from causing undesired operation of said heat-responsive element with attendant failure of said contacts to separate within the desired predetermined period of time.

3. A starting relay for discharge lamps comprising a thermal switch having a heat-responsive element, an electric heater operatively connected in circuit with the discharge lamp for heating said heat-responsive element to cause the latter to interrupt the circuit to said lamp after the lapse of a predetermined period of time,

and means carried by said heat-responsive element and operable to prevent heat generated by undue arcing upon interruption of the circuit for said lamp from causing undesired operation of said heat-responsive element by delaying operation thereof beyond a predetermined period of time.

4. A starting relay for discharge lamps comprising a casing, a thermal switch in said casing including a base provided with a heat-responsive element having one portion anchored at its endl to said base and the other portion being 1y movable with a contact adjacent the end thereof and including a stationary contact normally engaging the movable contact, an electric heater in juxtaposition to the anchored portion of said heat-responsive element for transmitting heat thereto to cause deflection of said heat-responsive element with separation of the movable contact from said stationary contact, means for connecting said electric heater and said heat-responsive element in a series circuit with the discharge lamp, and a projection carried by the movable portion of said heat-responsive element and engageable with said base upon heating of said heat-responsive element by undue arcing following separation of .said contacts to cause bowing of themovable portion of said heat-responsive element and prevent undesired -re-engagement oi said contacts immediately following their initial separation.

5. A starting relay for completing a circuit to a discharge lamp comprising a thermal switch including a base provided with a stationary contact and a heat-responsive element having one portion anchored at its end to said base and the other portion being provided with a movable contact adjacent the end thereof and normally tensioned into engagement with said stationary contact,

an electric heater in juxtaposition to the anchored portion of said heat-responsive element for transmitting heat thereto tocause deflection of said heat-responsive element with separation of said movable contact from said stationary contact and the contact-carrying portion .of said heat-responsive element being operable when heated by the heat generated upon closure of said contacts under load to increase the contact pressure thereof with said stationary contact to eliminate chattering, a projection carried by the heatresponsive element adjacent the movable contact and engageable'with said base upon heating of said heat-responsive element by undue arcing following separation of said contacts to cause bowing of the portion of said heat-responsive element carrying the movable contact and prevent undesired re-engagement of said contacts following their initial separation, and means for connecting said heat-responsive element and said heater inseries in said circuit.

6. Athermal relay for starting discharge larnps of the fluorescent type comprising a base, a stationary contact carried by said base, a heatresponsive element having a portion anchored at one end to said base and another portion freely movable and having a contact aiiixed thereto adjacent the end thereof normally tensioned in engagement with said stationary contact, an electric resistance heater in juxtaposition to the anchored portion of said heat-responsive element for transmitting heat thereto to cause deflection of the anchored portion in one direction and movement of the other portion in an opposite direction with attendant separation of said conengagement of said contacts following their initial separation. v

'7. A thermal relay for starting discharge lamps of the fluorescent type comprising a base, a stationary contact carried by said base, a heat-responsive element having a portion anchored at one end to said base and another portion freely movable and having a contact afilxed adjacent the end thereof normally tensioned in engagement with said stationary contact, an electric resistance'heater in juxtaposition to the. anchored portion of said heat-responsive element for transmitting heat thereto to cause deflection of the anchored portion in one direction and movement of the other portion in an opposite direction with attendant separation of said contacts, and the contact-carrying portion of said heat-responsive element being movable in the same direction as said anchored portion when heated by the heat generated upon the closure of said contacts under load to increase the contact pressure thereof with said stationary contact thus eliminating chattering, and a projection carried by the movable portion of said heat-responsive element and engageable with said base upon heating of said contact-carrying portion by undue arcing following separation of said contacts to cause bowing of the contact-carrying portion of their initial separation.

campus rrnongxms. 

